As a steering apparatus for applying a steering angle to steered wheel (normally, front wheels except in the case of special vehicles such as a forklift), construction as illustrated in FIG. 27 is well known. In this steering apparatus, a steering shaft 3 is supported on the inner-diameter side of a cylindrical steering column 2 that is supported by the vehicle 1 so as to be able to rotate. A steering wheel 4 is fastened to the rear end section of the steering shaft 3 that protrudes further toward the rear than the opening on the rear end of the steering column 2. As the steering wheel 4 is rotated, this rotation is transmitted to an input shaft 8 of a steering gear unit 7 by way of the steering shaft 3, a universal joint 5a, an intermediate shaft 6 and a universal joint 5b. As the input shaft 8 rotates, a pair of tie rods 9 that are located on both sides of the steering gear unit 7 are pushed and pulled, and a steering angel is applied to the pair of left and right steered wheels according to the amount that the steering wheel 4 is operated.
In the construction illustrated in FIG. 27, in order to make it possible to adjust the forward-backward position of the steering wheel 4, a steering column 2 and a steering shaft 3 that can extend and contract are used. Moreover, the steering column 2 and steering shaft 3 comprise a mechanism for making it possible to protect the driver when the body of the driver collides with the steering wheel 4 during a secondary collision that occurs with during a collision accident after the automobile collides with another automobile in a primary collision, by absorbing the impact energy during this secondary collision and allowing the steering wheel 4 to displace in the forward direction. More specifically, construction is employed wherein the steering shaft 3 that supports the steering wheel 4 is supported by the vehicle body 1 so as to be able to displace in the forward direction due to an impact load in the forward direction during a secondary collision. In the construction illustrated in FIG. 27, the steering shaft 3 is composed of an outer tube 11 and an inner shaft, and together with the outer tube 11 being able to displace in the forward direction while the entire length of the steering shaft 3 contracts due to an impact load during a secondary collision, the steering column 2 that supports the steering shaft 3 is composed of an outer column 10 and an inner column, and this outer column 10 is supported by the vehicle body 1 so as to be able to displace in the forward direction while the entire length of the steering column 2 contracts. The forward-backward position of the outer column and inner column of this extending and contracting type of steering column, and the outer tube and inner shaft of this steering shaft can also be opposite that of the construction illustrated in the figure.
On the other hand, as measures against theft of the automobile, an automobile may comprise various kinds of anti-theft apparatuses. As one of these anti-theft apparatus, a steering lock apparatus that makes it impossible to operate the steering wheel except when a proper key is used is in widespread use. FIG. 28 illustrates an example of construction of a steering lock apparatus that is disclosed in JP 2008-265646 (A). The steering apparatus 12 is provided with a lock unit 13 in part of the steering column 2a, and a key-lock collar 15, in which an engaging concave section 14 is formed in at least one location in the circumferential direction, is fitted around and fastened to a position of the steering shaft 3a, the phase in the axial direction of which coincides with that of the lock unit 13. During operation (when the key is locked), the tip end section of a lock pin 16 of the lock unit 13 is caused to displace in a direction toward the inner-diameter side of the steering column 2a through a lock through hole 17 that is formed in the middle section in the axial direction of the steering column 2a, and by engaging with the engaging concave section 14, makes it practically impossible for the steering shaft 3a to rotate.
When this kind of steering lock apparatus 12 is assembled in a steering apparatus, the lock unit 13 is provided on the outer-diameter side of the steering column 2a, and the key-lock collar 15 is provided on the inner-diameter side of the steering column 2a. Therefore, in order to place the key-lock collar 15 on the inner-diameter side of the steering column 2a so as to be able to rotate, and in order to make it possible for the lock pin 16 and the key-lock collar 12 to engage or disengage without an excessive stroke of the lock pin 16, it is necessary to make at least the outer diameter of the portion of the steering column 2a where the steering lock apparatus is assembled small, and to make the inner diameter large, and to make the thickness of this portion of the steering column 2a thin.
FIG. 29 illustrates an outer column 10a of a steering column that is disclosed in JP 2007-223383 (A). Inside one end section (left end section in FIG. 29) in the axial direction of the outer column, fitted is the other end section of the cylindrical inner column, so that relative displacement in the axial direction is possible. The outer column 10a is made of a light alloy such as an aluminum alloy, or magnesium alloy, and is integrally formed by casting, and a lock through hole 17a for assembling a steering lock apparatus 12 such as illustrated in FIG. 28 is provided in the middle section in the axial direction. When the thickness of this kind of outer column 10a is thin, there is a possibility that the strength of the outer column 10a that is necessary when the steering lock apparatus 12 is operated may not be sufficiently maintained. In other words, when the lock pin 16 that protrudes through the lock through hole 17a toward the inner-diameter side of the outer column 10 is engaged with the engaging concave section 14 (see FIG. 28) on the key-lock collar 15, and an attempt is made to rotate the steering wheel 4 (see FIG. 27) with a large force, an excessively large force is applied to the perimeter edge section of the lock through hole 17a, and there is a possibility that this perimeter edge section may deform. It is feasible to form the outer column 10a using an iron alloy, however, a problem occurs in that the overall weight of the steering column increases.